The present invention relates to a camshaft phaser for controlling the phase relationship between the crankshaft and a camshaft of an internal combustion engine; more particularly, to a vane-type phaser having a spring for biasing its rotor toward an extreme position; and most particularly, to a phaser wherein such a bias spring is disposed outside the rotor chamber for easy and reliable installation.
Camshaft phasers for varying the phase relationship between the pistons and the valves of an internal combustion engine are well known. Some prior art camshaft phasers include a torque bias spring within the rotor chamber to bias the rotor at rest toward an extreme rotational position; see, for example, U.S. Pat. No. 6,276,321 B1. Typically, such a spring must be accommodated within a well within the rotor hub, thus limiting the maximum possible diameter of the spring. The spring design is further compromised by requiring the spring hooks to be a small radius when the main coils are at a larger radius, which results in undesirably high stress levels in the spring wire and potentially difficult manufacturing processes. Further, the spring may be damaged or mis-installed during assembly, and correct installation cannot be verified visually after the rotor chamber is closed by the cover plate.
What is needed is a spring arrangement wherein spring diameters greater than the rotor diameter are available to optimize design of a vane-type phaser, and wherein spring installation is simple and easily verified after the rotor chamber is closed.
It is a principal object of the present invention to provide an improved camshaft phaser wherein a rotor torque bias spring has a radius greater than the radius of the rotor hub such that the size of the spring may be optimized.
It is a further object of the present invention to provide a phaser having an optimized torque bias spring.
It is a still further object of the invention to provide a phaser wherein installation of a rotor torque bias spring during phaser assembly is both simple and easily verifiable after closure of the rotor chamber.
Briefly described, a torque bias coil spring for a camshaft phaser is disposed on the outside of a cover plate for the rotor chamber. A first and passive tang of the spring is engaged by a fixed first stop, for example, a phaser binder bolt on the periphery of the stator. A second stop connected to the rotor, for example, a locking pin mechanism (first embodiment) or a target wheel (second embodiment), extends from the rotor chamber through the cover plate for engaging a second and active tang of the spring. The spring thus is able to follow the rotary motion of the rotor within the phaser stator and to apply bias of the rotor toward a predetermined rotational extreme, for example fully advanced although the spring load can be sized to balance or favor one direction or the other. As the rotor is commanded toward the opposite extreme position by the phaser controller, the spring load increases, which decreases the rate of response in that direction but increases the rate of response in the opposite direction. The spring is easily and reliably mounted onto the first and second stops after the rotor chamber has been assembled and the cover plate is in place and bolted down. A significant advantage over prior art springs disposed within the rotor chamber is that, by properly selecting the radial locations of the first and second stops and the diameter of the coils, the bias spring may be significantly larger in diameter than the rotor hub, a substantial limitation of prior art cam phasers having internal bias springs.
Further, with an external bias spring in accordance with a second embodiment, a prior art die cast cover, a spacer, and two dowel pins can be eliminated. The die cast cover may be replaced by a simple stamped cover. The fixed end of the spring is hooked to a stator bolt, and the moving end is fixed to a target wheel mechanism which rotates with the rotor and camshaft. This arrangement not only eliminates or simplifies several components but also increases available space for the spring, permitting use of a more robust spring with a lower spring rate within the overall axial length of a prior art phaser.